The invention relates to a preferably once recordable optical data storage medium containing a diaza hemicyanine dye as the light-absorbing compound in the information layer, and to a process for its production.
Recordable optical data storage media using special light-absorbing substances or mixtures thereof are particularly suitable for use in high-density recordable optical data storage media which operate with blue laser diodes, and in particular GaN or SHG laser diodes (360-460 nm), and/or for use in DVD-R or CD-R discs, which operate with red (635-660 nm) or infrared (780-830 nm) laser diodes, and the application of the above-mentioned dyes to a polymer substrate, in particular polycarbonate, by spin-coating or vapour deposition.
There has recently been an enormous growth in the sales of recordable compact discs (CD-R, 780 nm), which represent the technically established system.
The next generation of optical data storage mediaxe2x80x94DVDsxe2x80x94is currently being introduced onto the market. By using shorter-wave laser radiation (635 to 660 nm) and a higher numerical aperture NA, the storage density can be increased. The recordable format is in this case the DVD-R.
Today, optical data storage formats which use blue laser diodes (based on GaN, JP 08191171 or Second Harmonic Generation SHG JP 09050629) (360 nm to 460 nm) with a high laser power, are being developed. Recordable optical data storage media will therefore also be used in this generation. The achievable storage density depends on the focussing of the laser spot in the information plane. The spot size is proportional to the laser wavelength xcex/NA. NA is the numerical aperture of the objective lens used. The aim is to use the smallest possible wavelength xcex for obtaining the highest possible storage density. Based on semiconductor laser diodes, 390 nm are presently possible.
The patent literature describes dye-based recordable optical data storage media which are equally suitable both for CD-R and DVD-R systems (JP-A 11 043 481 and JP-A 10 181 206). In order to obtain high reflectivity, a high modulation level of the readout signal and sufficient sensitivity during recording, use is made of the fact that the IR wavelength 780 nm of the CD-R is located at the base of the long-wavelength slope of the absorption peak of the dye and the red wavelength 635 nm or 650 nm of the DVD-R is located at the base of the short-wavelength slope of the absorption peak of the dye. In JP-A 02 557 335, JP-A 10 058 828, JP-A 06 336 086, JP-A 02 865 955, WO-A 09 917 284 and U.S. Pat. No. 5,266,699 this concept is extended to cover the working wavelength range of 450 nm on the short-wavelength slope and the red and IR range on the long-wavelength slope of the absorption peak.
In addition to the above-mentioned optical properties, the recordable information layer consisting of light-absorbing organic substances must have a morphology which is as amorphous as possible, in order to keep the noise signal during recording or reading as small as possible. For this purpose it is particularly preferable, when applying the substances by spin-coating from a solution or by vapour deposition and/or sublimation, to prevent crystallization of the light-absorbing substances during the subsequent top-coating with metallic or dielectric layers in vacuo.
The amorphous layer of light-absorbing substances should preferably have high thermal stability, since otherwise additional layers of organic or inorganic material applied by sputtering or vapour deposition onto the light-absorbing information layer form blurred boundaries due to diffusion and thus have an adverse effect on the reflectivity. In addition, if a light-absorbing substance has inadequate thermal stability at the boundary to a polymeric substrate, it can diffuse into the latter and again have an adverse effect on the reflectivity.
If the light-absorbing substance has too high a vapour pressure, it can sublime during the above-mentioned sputtering or vapour deposition of additional layers in a high vacuum and thus reduce the desired layer thickness. This in turn has a negative effect on reflectivity.
The object of the invention is therefore to provide suitable compounds which meet the high demands (such as light stability, a favourable signal-to-noise ratio, damage-free application to the substrate material, etc.) for use in the information layer of a recordable optical data storage medium, in particular for high-density recordable optical data storage formats in a laser wavelength range of 340 to 680 nm.
Surprisingly, it has been found that light-absorbing compounds from the diaza hemicyanine group of dyes are particularly suitable for satisfying the above-mentioned requirement profile.
The invention therefore relates to an optical data storage medium containing a preferably transparent substrate which has optionally already been coated with one or more reflecting layers and onto the surface of which a photorecordable information layer, optionally one or more reflecting layers and optionally a protective layer or an additional substrate or a top layer are applied, which data storage medium can be recorded on and read using blue or red light, preferably laser light, wherein the information layer contains a light-absorbing compound and optionally a binder, characterized in that at least one diaza hemicyanine dye is used as the light-absorbing compound.
Blue laser light is particularly preferred.
The light-absorbing compound should preferably be thermally modifiable. Preferably the thermal modification is carried out at a temperature of  less than 600xc2x0 C., particularly preferably at a temperature of  less than 400xc2x0 C., very particularly preferably at a temperature of  less than 300xc2x0 C., and in particular at a temperature of  less than 200xc2x0 C. Such a modification can for example be the decomposition or chemical modification of the chromophoric centre of the light-absorbing compound.
A diaza hemicyanine of the formula (I) is preferred 
in which
K represents a radical of the formulae (II) to (IV) 
X1 represents O or S,
X2 represents O, S, CH or Nxe2x80x94R2,
X3 represents N, CH or Cxe2x80x94CN,
R1, R2 and R12 independently of one another represent C1- to C16-alkyl, C3- to C6-alkenyl, C5- to C7-cycloalkyl or C7- to C16-aralkyl,
A together with X2 and the C-atom bound therebetween represents a five-membered aromatic or quasi-aromatic heterocyclic ring which can contain 1 to 4 hetero atoms and/or can be benzo- or naphtho-fused and/or substituted by non-ionic radicals,
R3, R4, R5 and R6 independently of one another represent hydrogen, C1- to C16-alkyl, C4- to C7-cycloalkyl, C7- to C16-aralkyl or a heterocyclic radical or
NR3R4 or NR5R6 independently of one another represent a five- or six-membered saturated ring which is attached via N and can additionally contain an N or O atom and/or be substituted by non-ionic radicals,
R7 represents hydrogen, C1- to C16-alkyl, C1- to C16-alkoxy or halogen or
R7 and R5 form a two- or three-membered bridge which can contain an O or N atom and/or be substituted by non-ionic radicals,
R8 represents hydrogen, C1- to C16-alkyl, C1- to C16-alkoxy, halogen, cyano, C1- to C4-alkoxycarbonyl, Oxe2x80x94COxe2x80x94R10, NHxe2x80x94COxe2x80x94R10, Oxe2x80x94SO2xe2x80x94R10 or NHxe2x80x94SO2xe2x80x94R10,
R9 represents hydrogen, C1- to C4-alkyl or C6- to C10-aryl,
R10 represents hydrogen, C1- to C16-alkyl, C4- to C7-cycloalkyl, C7- to C16-aralkyl, C1- to C16-alkoxy, mono- or bis-C1- to C16-alkylamino, C6- to C10-aryl, C6- to C10-aryloxy, C6- to C10-arylamino or a heterocyclic radical,
R11 represents hydrogen, C1- to C4-alkyl or C6- to C10-aryl and
Anxe2x88x92 represents an anion.
Suitable non-ionic radicals are for example C1- to C4-alkyl, C1- to C4-alkoxy, halogen, cyano, nitro, C1- to C4-alkoxycarbonyl, C1- to C4-alkylthio, C1- to C4-alkanoylanino, benzoylamino, mono- or di-C1- to C4-alkylamino.
Alkyl, alkoxy, aryl and heterocyclic radicals can optionally contain additional radicals such as alkyl, halogen, nitro, cyano, COxe2x80x94NH2, alkoxy, trialkylsilyl, trialkyl-siloxy or phenyl, the alkyl and alkoxy radicals can be straight-chain or branched, the alkyl radicals can be partially halogenated or perhalogenated, the alkyl and alkoxy radicals can be ethoxylated or propoxylated or silylated, adjacent alkyl and/or alkoxy radicals on aryl or heterocyclic radicals can together form a three- or four-membered bridge and the heterocyclic radicals can be benzo-fused and/or quaternized.
The ring A of the formula 
particularly preferably represents thiazol-2-yl, benzothiazol-2-yl, benzoxazol-2-yl, benzimidazol-2-yl, imidazol-2-yl, pyrazol-3-yl, 1,3,4-triazol-2-yl, 1,3,4-thiadiazol-2-yl, 1,2,4-thiadiazol-5-yl, 2- or 4-pyridyl or 2- or 4-quinolyl, wherein the aforementioned rings can each be substituted by C1- to C6-alkyl, C1- to C6-alkoxy, fluorine, chlorine, bromine, iodine, cyano, nitro, C1- to C6-alkoxycarbonyl, C1- to C6-alkylthio, C1- to C6-acylamino, C6- to C10-aryl, C6- to C10-aryloxy, C6- to C10-arylcarbonylamino, mono- or di-C1- to C6-alkylamino, Nxe2x80x94C1- to C6-alkyl-Nxe2x80x94C6- to C10-arylamino, pyrrolidino, morpholino or piperazino.
In a particularly preferred form the diaza hemicyanines used are those of the formula (I),
in which
the ring A of the formula 
represents thiazol-2-yl, benzothiazol-2-yl, wherein X2 represents S and the aforementioned radicals can each be substituted by methyl, ethyl, methoxy, ethoxy, chlorine, cyano, methoxycarbonyl or ethoxycarbonyl, or represents 1,3,4-triazolyl or 1,3,4-thiadiazolyl, wherein X2 represents Nxe2x80x94R2 or S, respectively, and the aforementioned radicals can each be substituted by methyl, ethyl, phenyl, methoxy, ethoxy, methylthio, ethylthio, amino, anilino, dimethylamino, diethylamino, dipropylamino, dibutylamino, N-methyl-N-cyanethylamino, N-methyl-N-hydroxy-ethylamino, N-methyl-N-phenylamino, di-(cyanethyl)amino, di-(hydroxyethyl)amino, cyanethylamino, hydroxyethylamino, pyrrolidino, piperidino, morpholino or a radical of the formula 
K represents a radical of the formulae (II), (III) or (IV),
X1 represents O or S,
X3 represents N, CH or Cxe2x80x94CN,
R1, R2 and R12 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenethyl, phenylpropyl, allyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, cyanopropyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl or ethoxyethyl,
R3, R4, R5 and R6 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenethyl, phenylpropyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, cyanopropyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl, acetoxyethyl, propionyloxyethyl or a radical of the formula 
and R3 and R5 can additionally represent hydrogen or
NR3R4 and NR5R6 independently of one another represent pyrrolidino, piperidino, N-methylpiperazino, N-ethylpiperazino, N-hydroxyethylpiperazino or morpholino,
R7 represents hydrogen, methyl, methoxy or chlorine or
R7; R5 represent a xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)3xe2x80x94, xe2x80x94C(CH3)xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94 or xe2x80x94Oxe2x80x94(CH2)2xe2x80x94 bridge,
R8 represents hydrogen, methyl, methoxy or chlorine,
R9 represents hydrogen,
R11 represents hydrogen, methyl or phenyl and
Anxe2x88x92 represents an anion.
Suitable anions Anxe2x88x92 are all monovalent anions or one equivalent of a polyvalent anion. Preferably the anions are colourless. Suitable anions are, for example, chloride, bromide, iodide, tetrafluoroborate, perchlorate, hexafluorosilicate, hexafluorophosphate, methosulphate, ethosulphat, C1- to C10-alkanesulphonate, C1- to C10-perfluoroalkane sulphonate, C1- to C10-alkanoate optionally substituted by chlorine, hydroxyl or C1- to C4 alkoxy, benzene sulphonate, naphthalene sulphonate or biphenyl sulphonate optionally substituted by nitro, cyano, hydroxyl, C1- to C25-alkyl, perfluoro-C1- to C4-alkyl, C1- to C4-alkoxycarbonyl or chlorine, benzene disulphonate, naphthalene disulphonate or biphenyl disulphonate optionally substituted by nitro, cyano, hydroxyl, C1- to C4-alkyl, C1- to C4-alkoxy, C1- to C4-alkoxycarbonyl or chlorine, benzoate optionally substituted by nitro, cyano, C1- to C4-alkyl, C1- to C4-alkoxy, C1- to C4-alkoxycarbonyl, benzoyl, chlorobenzoyl or toluoyl, the anion of naphthalenedicarboxylic acid, diphenyl ether disulphonate, tetraphenyl borate, cyanotriphenyl borate, tetra-C1- to C20-alkoxyborate, tetraphenoxyborate, 7,8- or 7,9-dicarba-nido-undecaborate(1-) or (2-), which are optionally substituted on the B- and/or C-atoms by one or two C1- to C12-alkyl or phenyl groups, dodecahydro-dicarbadodecaborate(2-) or Bxe2x80x94C1- to C12-alkyl-C-phenyl-dodecahydro-dicarbadodecaborate(1-).
Bromide, iodide, tetrafluoroborate, perchlorate, methane sulphonate, benzene sulphonate, toluene sulphonate, dodecylbenzene sulphonate and tetradecane sulphonate are preferred.
In a very particularly preferred form the diaza hemicyanines used are those of the formulae (VI) to (IX) 
in which
R1 and R2 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
R5 and R6 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl or acetoxyethyl or
NR5R6 represents pyrrolidino, piperidino or morpholino,
R7 represents hydrogen or
R7; R5 represent a xe2x80x94(CH2)2xe2x80x94, xe2x80x94C(CH3)xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94 or xe2x80x94Oxe2x80x94(CH2)2xe2x80x94 bridge,
R8 represents hydrogen,
R13, R14 and R15 independently of one another represent hydrogen, methyl, methoxy, chloro, nitro or cyano,
R16 and R17 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl, acetoxyethyl or phenyl and
R16 additionally represents hydrogen or
NR16R17 represents pyrrolidino, piperidino or morpholino, and
Anxe2x88x92 represents tetrafluoroborate, perchlorate, hexafluorosilicate, hexafluorophosphate, iodide, rhodanide, cyanate, hydroxy acetate, methoxy acetate, lactate, citrate, methane sulphonate, ethane sulphonate, benzene sulphonate, toluene sulphonate, butylbenzene sulphonate, chlorobenzene sulphonate, dodecylbenzene sulphonate or naphthalene sulphonate,
wherein all alkyl radicals can be branched.
In a very particularly preferred form the diaza hemicyanines used are those of the formulae (X) to (XIII) 
in which
R1 and R2 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
X1 represents O and
X3 represents CH or
X1 represents S and
X3 represents N, CH or Cxe2x80x94CN,
R3 and R4 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl or acetoxyethyl or
NR3R4 represents pyrrolidino, piperidino or morpholino,
R9 represents hydrogen,
R13, R14 and R15 independently of one another represent hydrogen, methyl, methoxy, chloro, nitro or cyano,
R16 and R17 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl, acetoxyethyl or phenyl and
R16 additionally represents hydrogen or
NR16R17 represents pyrrolidino, piperidino or morpholino, and
Anxe2x88x92 represents tetrafluoroborate, perchlorate, hexafluorosilicate, hexafluorophosphate, iodide, rhodanide, cyanate, hydroxy acetate, methoxy acetate, lactate, citrate, methane sulphonate, ethane sulphonate, benzene sulphonate, toluene sulphonate, butylbenzene sulphonate, chlorobenzene sulphonate, dodecylbenzene sulphonate or naphthalene sulphonate,
wherein all alkyl radicals can be branched.
In a very particularly preferred form the diaza hemicyanines used are those of the formulae (XIV) to (XVII) 
in which
R1, R2 and R12 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl or a radical of the formula 
R13, R14 and R15 independently of one another represent hydrogen, methyl, methoxy, chloro, nitro or cyano,
R16 and R17 independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, cyclohexyl, chloroethyl, cyanoethyl, hydroxyethyl, 2-hydroxypropyl, methoxyethyl, ethoxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl, acetoxyethyl or phenyl and
R16 additionally represents hydrogen or
NR16R17 represents pyrrolidino, piperidino or morpholino,
R11 represents hydrogen, methyl or phenyl and
Anxe2x88x92 represents tetrafluoroborate, perchlorate, hexafluorosilicate, hexafluorophosphate, iodide, rhodanide, cyanate, hydroxy acetate, methoxy acetate, lactate, citrate, methane sulphonate, ethane sulphonate, benzene sulphonate, toluene sulphonate, butylbenzene sulphonate, chlorobenzene sulphonate, dodecylbenzene sulphonate or naphthalene sulphonate,
wherein all alkyl radicals can be branched.
In a very particularly preferred form the diaza hemicyanines used are those of the formulae (IX), (XIII) and (XVII).
For a recordable optical data storage medium according to the invention which is recorded on and read using light from a blue laser, such diaza hemicyanine dyes are preferred whose absorption maximum xcexmax2 is in the range from 420 to 550 nm, wherein the wavelength xcex1/2 at which the extinction on the short-wavelength slope of the absorption maximum of the wavelength xcexmax2 is half the extinction value at xcexmax2, and the wavelength xcex1/10, at which the extinction on the short-wavelength slope of the absorption maximum of the wavelength xcexmax2 is a tenth of the extinction value at xcexmax2, are preferably in each case no further than 50 nm away from each other. Preferably such a diaza hemicyanine dye does not display a shorter-wave maximum xcexmax1 at a wavelength below 350 nm, particularly preferably below 320 nm, and very particularly preferably below 290 nm.
Preferred diaza hemicyanine dyes are those with an absorption maximum xcexmax2 of 410 to 530 nm.
Particularly preferred diaza hemicyanine dyes are those with an absorption maximum xcexmax2 of 420 to 510 nm.
Very particularly preferred diaza hemicyanine dyes are those with an absorption maximum xcexmax2 of 430 to 500 nm.
In these diaza hemicyanine dyes xcex1/2 and xcex1/10, as defined above, are preferably no further than 40 nm, particularly preferably no further than 30 nm, and very particularly preferably no further than 20 nm away from each other.
For a recordable optical data storage medium according to the invention which is recorded on and read using light from a red laser, such diaza hemicyanine dyes are preferred whose absorption maximum xcexmax2 is in the range from 500 to 650 nm, wherein the wavelength xcex1/2 at which the extinction on the long-wavelength slope of the absorption maximum of the wavelength xcexmax2 is half the extinction value at xcexmax2, and the wavelength xcex1/10, at which the extinction on the long-wavelength slope of the absorption maximum of the wavelength xcexmax2 is a tenth of the extinction value at xcexmax2, are preferably in each case no further than 50 nm away from each other. Preferably such a diaza hemicyanine dye does not display a longer-wave maximum xcexmax""at a wavelength below 750 nm, particularly preferably below 800 nm, and very particularly preferably below 850 nm.
Preferred diaza hemicyanine dyes are those with an absorption maximum xcexmax2 of 530 to 630 nm.
Particularly preferred diaza hemicyanine dyes are those with an absorption maximum xcexmax2 of 550 to 620 nm.
Very particularly preferred diaza hemicyanine dyes are those with an absorption maximum xcexmax2 of 580 to 610 nm.
In these diaza hemicyanine dyes xcex1/2 and xcex1/10, as defined above, are preferably no further than 40 nm, particularly preferably no further than 30 nm, and very particularly preferably no further than 20 nm away from each other.
At the absorption maximum xcexmax2 the diaza hemicyanine dyes have a molar extinction coefficient xcex5 of  greater than 30000 l/mol cm, preferably  greater than 40000 l/mol cm, particularly preferably  greater than 50000 l/mol cm and very particularly preferably  greater than 70000 l/mol cm.
The absorption spectra are, for example, measured in solution.
Suitable diaza hemicyanines having the required spectral properties are in particular those in which the change in the dipole moment xcex94xcexc=|xcexcgxe2x88x92xcexcag|, i.e. the positive difference between the dipole moments in the ground state and the first excited state is as small as possible, i.e. preferably  less than 5 D, and particularly preferably  less than 2 D. A method of determining such a change in the dipole moment xcex94xcexc is described, for example, in F. Wxc3xcrthner et al., Angew. Chem. 1997, 109, 2933 and in the literature cited therein. Low solvatochromism (methanol/methylene chloride) is also a suitable criterion for selection. Preferred diaza hemicyanines are those whose solvatochromism xcex94xcex=|xcexmethylene chloridexe2x88x92xcexmethanol|, i.e. the positive difference between the absorption wavelengths in the solvents methylene chloride and methanol, is  less than 25 nm, particularly preferably  less than 15 nm, and very particularly preferably  less than 5 nm.
Diaza hemicyanines of the formulae (I) and (VI) to (XVII) are known, for example, from BE 825 455,DE-OS 1 044 023, DE-OS 2 811 258, DE-OS 1 163 775.
Another part of the invention are diaza hemicyanines of formula (I), wherein K means a radical of formula (III) and the other residues have the above meaning. Another special part of the invention are diaza hemicyanines of the formulae (X), (XI), (XII) or (XIII), wherein the residues have the above meaning.
The light-absorbing substances described guarantee sufficiently high reflectivity ( greater than 10%) of the optical data storage medium in the unrecorded state and sufficiently high absorption for the thermal degradation of the information layer upon spotwise illumination with focussed light, if the wavelength of the light is in the range from 360 to 460 nm and 600 to 680 nm. The contrast between the recorded and unrecorded areas of the data storage medium is effected by the change in reflectivity in terms of the amplitude as well as the phase of the incident light as a result of the changed optical properties of the information layer following thermal degradation.
The diaza hemicyanine dyes are preferably applied to the optical data storage medium by spin-coating or vacuum coating. The diaza hemicyanines can be mixed with other dioaza hemicyanines or with other dyes having similar spectral properties. The information layer can contain additives in addition to the diaza hemicyanine dyes, such as binders, wetting agents, stabilizers, diluents and sensitizers as well as other constituents.
In addition to the information layer, the optical data storage medium can contain other layers such as metal layers, dielectric layers and protective layers. Metals and dielectric layers are used, for example, for adjusting the reflectivity and the thermal balance. Depending on the laser wavelength, the metals can be gold, silver or aluminium, etc. Dielectric layers are, for example, silicon dioxide and silicon nitride. Protective layers are, for example, photocurable surface coatings, adhesive layers and protective films.
Adhesive layers can consist of a pressure-sensitive material.
Pressure-sensitive adhesive layers consist mainly of acrylic adhesives. Nitto Denko DA-8320 or DA-8310, which are disclosed in the patent JP-A 11-273147, can, for example, be used for this purpose.
The optical data storage medium has, for example, the following layer assembly (cf. FIG. 1): a transparent substrate (1), optionally a protective layer (2), an information layer (3), optionally a protective layer (4), optionally an adhesive layer (5) and a top layer (6).
Preferably, the optical data storage medium assembly can contain:
a preferably transparent substrate (1), onto whose surface at least one photorecordable information layer (3), which can be recorded on using light, preferably laser light, optionally a protective layer (4), optionally an adhesive layer (5) and a transparent top layer (6) are applied;
a preferably transparent substrate (1), onto whose surface a protective layer (2), at least one information layer (3) which can be recorded on using light, preferably laser light, optionally an adhesive layer (5) and a transparent top layer (6) are applied;
a preferably transparent substrate (1), onto whose surface optionally a protective layer (2), at least one information layer (3) which can be recorded on using light, preferably laser light, optionally a protective layer (4), optionally an adhesive layer (5) and a transparent top layer (6) are applied;
a preferably transparent substrate (1), onto whose surface at least one information layer (3) which can be recorded on using light, preferably laser light, optionally an adhesive layer (5) and a transparent top layer (6) are applied.
Alternatively, the optical data storage medium has for example the following layer assembly (cf. FIG. 2): a preferably transparent substrate (11), an information layer (12), optionally a reflecting layer (13), optionally an adhesive layer (14) and an additional, preferably transparent, substrate (15).
The invention also relates to optical data storage media according to the invention which are recorded on using blue or red light, in particular laser light.
The following examples illustrate the subject matter of the invention: